if I had c section like 9 month ago, I'm pregnant with 4 week I will deliver baby before the 40…

Do you mean "will I"?

yes

No not necessarily, having a c section doesn't mean you'll have the next sooner...however, often times second babies come a little bit earlier anyways, and depending on why you got your c section the first time you can attempt to have a vaginal birth the second time around, called a VBAC (vaginal birth after cesarean).

And what I mean by a little bit sooner is like maybe a week....so if you went into labor with the first at 40 weeks with the second you could go into labor at 39 weeks. It's not a guarantee, but it's likely.